This invention relates to an externally ignited four cycle internal combustion engine in which the fuel-air mixture is formed outside of at least one cylinder. The present invention is concerned, more particularly, with such an internal combustion engine in which the cylinder head of each cylinder is equipped with one inlet valve and one outlet valve. The outlet to be closed by the outlet valve is located in the proper portion of a swirl (turbulence or vortex) chamber within this cylinder, which is open in the direction of the interior volume of the cylinder below the cylinder head. The height of the swirl chamber is typically less than its maximum diameter.
Numerous engines with swirl chambers are known. Until the present time, the fuel for these engines had always been injected directly into the swirl chamber. In the short time available, the fuel can be mixed with the air substantially better when the fuel is injected directly into or from a swirl chamber. However, direct fuel injection requires expensive injection pumps and hence is limited to special cases in which the extra costs appear to be justified. There have also been many instances of swirl chambers used with direct fuel injection into the swirl chamber for the purpose of creating a stratified charge immediately prior to the ignition with the goal of achieving cleaner combustion.
The possibility of supplying these constructionally simple engines with a fuel/air mixture prepared outside of the cylinder has previously been part of the state of the art on paper only because no advantages could heretofore be achieved by comparison with internal combustion engines without swirl chambers.